The present invention relates generally to the field of electrical connectors, and, more particularly, to a Zero Insertion Force (ZIF) socket assembly.
Integrated circuits (ICs) are becoming smaller, more complex, and more prevalent. It is common for a modern electronic appliance, such as a computer, a video cassette recorder, or even a refrigerator, to have several IC components attached to a circuit board. Each IC is generally delivered as an enclosed package with a pin grid array (PGA) interface. The PGA interface is a set of electrically conductive pins arranged in a pattern, where each pin is an electrical connection to the functional portion of the IC. In order to install the IC in an electronic appliance, the pins must be electrically connected to appliance""s main circuit board. It is thus desirable for there to be a simple mechanism that permits the IC to be quickly and easily attached to the circuit board, while minimizing the risk of damage.
One device that permits a simple, fast connection between an IC and a circuit board is a Zero Insertion Force (ZIF) socket assembly. A ZIF socket assembly is a device having set of contacts in electrical connection with the circuit board, where the contacts are disposed in a set of sockets. The device is arranged such that the pins of the IC can be inserted into the sockets without touching the contacts so that the pins do not encounter frictional resistance as they are inserted. Subsequent to the insertion of the pins, the device brings the pins and contacts into electrical connection, such that electrical impulses can flow freely between the pins and the circuit board by way of the contacts.
A number of ZIF socket devices have been proposed. A typical ZIF socket assembly has a contact which either touches the pin at a bend (see, e.g., Griffin, U.S. Pat. No. 4,375,309) or which crosses the pin so as to touch the pin only at a single point (see, e.g., Bright, et al., U.S. Pat. No. 4,988,310). These devices are not well-adapted for small scale PGAs (e.g., a PGA having pins arranged in a grid on centers spaced 0.050 inches apart) because the electrical contact region formed is small, and its effective size may be reduced even further by debris and contaminants which interfere with electrical conduction. While this type of connection may be acceptable for large-scale PGAs, when the PGA is miniaturized to the scale of about 0.050 inch centers, the small electrical contact region that results when the pin and contact touch only at a point may cause the quality of the electrical connection to be poor. By allowing the contact and the pin to touch each other over a continuous length of their surfaces, as well as wiping the contact and pin against each other to remove some debris and contaminants, the quality of the electrical connection for small-scale PGAs is improved.
A ZIF socket assembly in accordance with the invention allows for a small (e.g. 0.050 inch centers) PGA package to be brought into low-resistance electrical connection with a circuit board without the pins of the PGA encountering frictional resistance as contact is made. The ZIF socket assembly comprises a top plate and a base plate, each made of an electrically insulating material. The base plate has a plurality of contacts arranged in a pattern, each contact being disposed in an opening in the base plate. Each electrical contact has an adjoining tail which extends downward from the base plate and is electrically connectable to a circuit board. Each contact also has a portion that extends upward from the base plate which makes electrical contact with the pins of a PGA package that is to be received by the ZIF socket assembly.
The top plate, which has a plurality of apertures arranged in the same pattern as the contacts, is slidably attached over the base plate, such that it can move between a first position and a second position. Each socket has a narrow upper portion and a wide lower portion. Each contact is received in the wide lower portion of a corresponding aperture. When the top plate is in the first position, a PGA package with pins arranged in the same pattern as the contacts and apertures can be inserted into the top plate through the narrow upper portions of the apertures. As the pins are inserted, the narrow portions of the sockets guide the pins past the contacts so that the pins do not touch the contacts, thereby allowing the pins to be inserted with substantially no frictional resistance.
After the pins have been inserted into the sockets, the top plate is slid over the base plate from the first position to the second position, thereby causing the pins and contacts to be pushed together. The ZIF socket assembly preferably includes either a handle-driven cam mechanism which provides the force necessary to slide the top plate from the first position to the second position, or a set of slits into which a flat-tipped screwdriver may be received to provide the necessary force. Each contact includes two straight portions joined at a bend. As each pin moves closer to a contact, it pushes against the bend and deflects the contact so as to bring one of the straight portions of the contact into vertical alignment with the surface of the pin, such that the straight portion and the pin are in physical connection over a continuous length of their respective surfaces. As the contact is being deflected and brought into physical contact with the pin, the contact wipes against the pin, thereby removing contaminants and debris from the electrical contact region. The continuous length over which contact is made, as well as the wiping action, combine to form a good, low-resistance electrical connection between pins and contacts.
Other features of the invention are described below.